His grandmother, Mary Mulelema, sells each bag, to be used to make concrete, for 10,000 kwacha, less than $3. Often, she said, it is the difference between eating and going hungry.

“Sometimes when he’s tired, I tell him to stop, but he helps me here most of the time,” she said. “We work every day, to make that powder. Sometimes we work Sunday, if we don’t go to church.”

Across the globe, the number of children forced to work is in sharp decline.

But sub-Saharan Africa, in places like Lusaka and for children like Alone, is the exception. Here, more than one in four children below age 14 works, whether full time or for a few hours a week, nearly the same percentage as the worldwide average in 1960.

It is by far the greatest proportion of working children in the world.

By the United Nations’ latest estimate, more than 49 million sub-Saharan children age 14 and younger worked in 2004, 1.3 million more than at the turn of the century just four years earlier.

Their tasks are not merely the housework and garden-tending common to most developing societies.

They are prostitutes, miners, construction workers, pesticide sprayers, haulers, street vendors, full-time servants, and they are not necessarily even paid for their labor.

Some are as young as 5 and 6 years old.

In Kenya, nearly a third of the coffee pickers were children, a 2001 World Bank Report found.

In Tanzania, 25,000 children worked in hazardous jobs on plantations and in mines.

Their numbers in Africa grow even as the ranks of child laborers are dropping by the millions in every other region of the world.

Child labor declines with prosperity, and so the region’s economic plight — 44 percent of sub-Saharan residents live on less than $1 a day, far and away the greatest share on earth — is a big reason.

But so are social mores that regard hard work by children as the norm, and conflicts that scatter families and kill breadwinners.

So is the staggering H.I.V. rate, which has created millions of orphans who must work to survive, and has forced millions more to work to support dying parents. In Zambia alone, a 2002 study by independent researchers for the United Nations concluded that AIDS had boosted the number of child laborers by up to 30 percent.

So is the region’s population explosion. Well over 4 in 10 people here are under age 15, compared with fewer than 2 in 10 in the developed world, according to the Population Reference Bureau, a nonprofit research organization.

With economic growth lagging births, manual labor is often the only way the newcomers can feed themselves.

Worldwide, the number of children who were already “economically active” by the age of 14 fell roughly 10 percent from 2000 to 2004, to about 191 million, according to the International Organization for Labor, a United Nations agency.

More impressive still, the number of young children laboring in the most dangerous jobs dropped by a third.

In Asia, the number of economically active children — meaning they worked beyond their chores, legally or not — dropped by five million in just four years.

In Latin America and the Caribbean, the decline was even more drastic, nearly 12 million. Indeed, sub-Saharan Africa was the only region where the number of working children did not fall.

“It’s like trying to empty a bathtub with a teaspoon while the tap is running,” said Birgitte Poulsen, the technical specialist for the International Labor Organization in Zambia. “If you want to tackle this, you have to recognize the magnitude of the problem, not just in terms of its size, but its complexity. It isn’t just due to instability and conflict and war. It’s poverty and H.I.V.-AIDS.”

Echoes of Oliver Twist

If the stereotype of child labor is an Oliver Twist world of sweatshops with youngsters hunched over sewing machines or metal presses, Africa’s reality is different.

A handful of Zambia’s child workers are clearly exploited by adults — for prostitution in cities, and perhaps as miners in the emerald-rich north, near the Democratic Republic of Congo.

The International Labor Organization says there are increasing reports of Zambian children being trafficked for work in construction and farming and as servants.

Overwhelmingly, though, what drives children into work is not greed but privation. Young people here largely work to feed themselves or their parents, or both.

Alone — a family name, like many in this part of the world, drawn from the English language — and his grandmother rise at about 6:30 a.m.

After washing, they make the half-hour walk to the quarry where they work, under a plastic tarp mounted on scavenged tree branches.

Alone describes his day in the most basic English: “I break the rocks. I get up early in the morning, before the sun rises. For breakfast, I drink tea sometimes. This morning, I didn’t eat. I’m hungry.”

After two hours, he walks to Tatwasha Basic School, a state-run institution near his home, for about four hours of classes.

Tatwasha, a grid of cinder-block buildings set on a yellow dirt courtyard, has 3,000 students. About 300 work in the quarries.

Maureen Chinjenge, the school’s stern headmistress, has a word for the quarry children: disoriented.

“Most of these children are orphans,” she said, “and in most cases, their performance is not good. For the most part, they don’t eat breakfast, and coming to classes they don’t concentrate. Things like clothing, they don’t have any, and the other children make fun of them.”

Their attendance, she says, is spotty. Many are latecomers; some first-graders are as old as 11.

Alone, a second-grader at age 9, fits that template well. Asked his teacher’s name, he fidgets for fully a minute, then answers ruefully, “I don’t remember.”

After school, he returns to the quarry where, sitting cross-legged on the ground, he attacks his pile of rocks for five more hours, until sunset.

A scab marked his left cheek, damage from a sliver of quartz-like rock that flew into his face after an especially hard strike.

Other stone-crushers complain of broken fingers, impaired vision or a “heavy chest,” an early sign of silicosis, but Alone says he has suffered no serious injuries beyond some smashed fingers and cut eyes.

“It’s a hard job; I hurt myself sometimes,” he said, but “I measure my size. I don’t break huge amounts. I do it according to my age.”

Beyond the physical cruelty and lost youth, sub-Saharan Africa’s child laborers are social and economic millstones on a region that can ill afford them.

They are poorly educated, badly fed, inadequately supervised by adults and far more likely to become illiterates whose children, like them, will toil in fields, tend roadside stands or crush rocks.

Already, a number of studies have documented increases in street children in sub-Saharan cities, many of them AIDS orphans forced into sidewalk vending, theft or selling sex to survive.

Photo

Children as young as 4 work six and seven days a week in quarries near Lusaka, Zambia, breaking stones into gravel sold at roadside stalls. Credit
Jeffrey Barbee for The New York Times

In Lusaka, a city of 1.2 million, “I don’t think it would come to more than 50,000, but the number is definitely growing,” said Yvonne Chilufya, a project manager for Jesus Cares Ministries, a Zambian organization that assists street children and other child laborers.

“We see a lot of child-headed households as a result of H.I.V.,” she added. “In other cases, you find the parents are both alive, but doing nothing, chronically ill. So the children are taking care of the parents. The parents send the children out to find food.”

The last time Zambia’s government counted, in 1999, it found nearly 600,000 child laborers between ages 5 and 17, roughly 9 in 10 of them on farms, the rest in the cities, working as vendors, domestics or laborers.

Zambia also has signed the two international conventions that set minimum ages for work and outlaw the most harmful forms of child labor.

In recent years, its news media have begun to expose dangerous working conditions for children, and its government has started to move against the most outlandish forms of labor.

But as elsewhere in Africa, Zambia’s stifling bureaucracy, its poverty, the AIDS epidemic and the sheer size of the task all work against success.

Ms. Poulsen, of the International Labor Organization, says the government’s efforts to weed out child labor would be reasonably good “if you have inspectors, cars and fuel.” Zambia has precious little of each.

“We’ve got lots and lots of good policies in this country,” she said. “But there’s no coordination. It’s difficult to staff basic social services — schools, clinics — because people keep dying” of AIDS.

Choosing a Way to Die

Chola J. Chabala, the Zambian assistant labor commissioner and the official charged with reducing child labor, says the number of children who work is growing despite his government’s efforts, especially in rural areas where oversight is weak.

“I do this job with a passion, but it is very depressing at the end of the day,” he said. “I’ve heard children who work as prostitutes say they would rather die from AIDS, because it is slower than dying of hunger.”

Crushing stone is ranked in international agreements as one of the worst forms of child labor, full of risks from flying rock fragments, misdirected hammers, repetitive motion injuries and years of inhaling dust.

Mrs. Chilufya, of Jesus Cares Ministries, says that in the last four years her group has taken close to 1,000 children from the quarries, placing them in the organization’s own schools and giving small loans to parents and caretakers to open more sustainable businesses, like roadside groceries.

But Lusaka has three major quarries, and although hundreds of children have been rescued and sent to schools, hundreds more have taken their place.

The quarries are sprawling outcrops of limestone or quartz-like rock that are hand-mined by hundreds of itinerants armed with hammers, shovels and sledges.

In places, they have dug as much as 20 feet below the surface, leaving lattices of surface paths between pits of algae-clogged rainwater, washbasins for the workers’ laundry.

The quarries have their own economy. Men split boulders into smaller chunks, then sell them by the barrow to women whose families reduce them to gravel and powder.

Homeless and unsupervised children, roaming the streets, hire themselves out at about 30 cents a day to help with the crushing.

The output goes on display beside highways — waist-high piles of gravel; old cement bags packed with crushed stone or powder. Construction crews buy the rocks and powder, then sell the cement bags back to the rock breakers.

It is a tiring, endlessly tedious task. Its practitioners work six and seven days a week, and they make almost nothing.

The two or three bags of rock powder that Alone can produce, at 10,000 kwacha per bag, are sold as a mixer for concrete, often to line swimming pools for Lusaka’s wealthier residents.

They are the most lucrative products his grandmother offers, almost enough to pay the $11 a month she needs for rent and access to the community water tap.

Sales of the gravel she produces earn barely enough money to buy corn meal and small, dried fish, called kapenta, that the two eat for dinner.

For Mrs. Mulelema, Alone is literally the difference between profit and loss, and a hair’s-breadth difference at that.

“We don’t eat breakfast every day,” she said. “At lunch we have sweet potatoes, and then we wait for supper.

“If I decide to have my breakfast, it means I won’t have anything for supper.”

Mrs. Mulelema once tried to open a food stand in the community market, but could not raise the cash.

Like virtually all the hundreds of Lusakans who crush stones, she says she does it because she has no choice.

“The business has no profit,” said Mwila Zulu, a 40-year-old mother of three girls. She has been crushing stone at a quarry in Lusaka’s industrial zone since the police shut down her unlicensed vegetable stand in the city’s downtown in 2002.

Mrs. Zulu’s husband died last year with symptoms that pointed to AIDS. Her daughters work at the quarry after school ends at noon, trying to fill the space he left. The youngest, Kunda and Mercy, break rocks with ball-peen hammers, the handles cut down to fit their hands.

By day’s end, their deep brown arms and faces wear a film of white quartz-like dust.

They are 7 and 8 years old.

“She started working with me in recent years,” Mrs. Zulu said of Kunda. “She couldn’t do anything when she was young, but now she’s grown, so she’s helping me.”

For 50,000 kwacha, or $15, a passing construction worker can buy a chest-high heap of gravel that took them three weeks to render.

But sales of that size are infrequent, sometimes once every two or three weeks, and money is short.

Mrs. Zulu said she did not waste time fretting over her daughters’ fate.

“If I feel pity for them,” she said, “what are they going to eat?”

Gavin du Venagecontributed reporting from Sedgefield, South Africa, for this article.

A version of this article appears in print on , on Page A1 of the New York edition with the headline: Africa Adds to Miserable Ranks of Child Workers. Order Reprints|Today's Paper|Subscribe